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Understanding LTE with MATLAB by Houman Zarrinkoub

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Chapter 6

MIMO

So far we have studied the modulation, scrambling, coding, channel modeling, and multicarrier transmission schemes used in the LTE (Long Term Evolution) standard. In this chapter we focus on its multi-antenna characteristics. The LTE and LTE-Advanced standards achieve high maximum data rates mainly as the result of incorporating many multi-antenna or MIMO (Multiple Input Multiple Output) techniques. LTE can be regarded as a MIMO–OFDM (Orthogonal Frequency Division Multiplexing) system, with MIMO multi-antenna configurations being combined with the OFDM multicarrier transmission scheme.

In general, multi-antenna transmission schemes map modulated data symbols to multiple antennas ports. In the OFDM transmission scheme, each antenna constructs the resource grid, generates the OFDM symbols, and transmits the signal. In a MIMO–OFDM system, the process of resource-grid mapping and OFDM modulation is repeated over multiple transmit antennas. Depending on the MIMO mode used, this multi-antenna extension may result in a boost in data rates or an improvement in the link quality.

In this chapter, we will first review MIMO algorithms of the first four transmission modes of the LTE standard. These transmission modes exploit two main MIMO techniques: (i) transmit diversity (techniques such as Space–Frequency Block Coding, SFBC) and (ii) spatial multiplexing with or without delay-diversity coding. As noted earlier, transmit diversity techniques improve the link quality and reliability ...

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